Depth stop instrument for use in spinal surgery

ABSTRACT

A disc preparation instrument for use in fusing spinal vertebrae comprises a modular scoring trial and a depth stop releasably attached to the scoring trial. The trial includes an elongate stem supporting a trial device at its distal tip. The trial device is insertable into a disc space and includes a rotatable rasp for scoring opposing vertebral endplates at a scored location. A stop, sized to engage an exterior surface of the vertebrae, is movable on the depth stop stem by rotation of an adjustment knob to a plurality of selectable distances between the proximal end of the trial device and the movable stop. An actuator releasably attached to the trial is operable to rotate the rasp. A plurality of modular trials, each having a trial device of different heights may be provided in a kit. Each scoring trial is selectively releasably attachable to a single depth stop.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 16/150,335, filed Oct. 3, 2018, now pending, which claims thebenefit of U.S. Provisional Patent Application No. 62/568,575, filedOct. 5, 2017, and U.S. Provisional Patent Application No. 62/570,179,filed Oct. 10, 2017, the entire contents of such applications beingincorporated by reference herein.

FIELD OF THE INVENTION

The subject invention relates generally to the field of spinalinstrumentation and more particularly to a spinal disc preparationinstrument for use in fusing together a superior vertebra and aninferior vertebra, the disc preparation instrument including a modularscoring trial and a releasable depth stop.

BACKGROUND OF THE INVENTION

Spinal implants such as interbody fusion devices are used to treatdegenerative disc disease and other damages or defects in the spinaldisc between adjacent vertebrae. The disc may be herniated or sufferingfrom a variety of degenerative conditions, such that the anatomicalfunction of the spinal disc is disrupted. Most prevalent surgicaltreatment for these conditions is to fuse the two vertebrae surroundingthe affected disc. In most cases, the entire disc will be removed,except for a portion of the annulus, by way of a discectomy procedure. Aspinal fusion device is then introduced into the intradiscal space andsuitable bone graft or bone substitute material is placed substantiallyin and/or adjacent the device in order to promote fusion between twoadjacent vertebrae.

One embodiment of a spinal device for cervical fusion is described inU.S. Patent Publication No. 2015/0202051, entitled “Spinal FusionSystem”, filed on Jan. 16, 2015 by Shigeru Tanaka et al. (the '051Application) and assigned to the same assignee as the subjectapplication. The entire contents of the '051 Application areincorporated herein by reference. The spinal fusion system described inthe '051 Application includes an interbody fusion cage, a fixation platewith deployable anchor blades, and an implanter. In a particulararrangement described in the '051 Application, the system may furtherinclude a trial/sizer tool including a set of trial/sizer instruments.Such instruments may incorporate a pre-scoring blade to break thevertebral endplate prior to insertion of the spinal implant into thedisc space and deployment of the blades into the endplates. As such, thetrial device may serve two purposes, namely to test a size for apotential interbody fusion cage implant and to prepare one or morevertebral endplate surfaces for receiving the implant.

Another example of a scoring trial particularly useful in cervicalfusion is shown and described in U.S. patent application Ser. No.15/454,287, entitled “Scoring Implant Trial and Implant Inserter forSpinal Fusion System”, filed on Mar. 9, 2017 by Andrew Bernhardt, Jr. etal. (the '287 Application) and assigned to the same assignee as thesubject application. The entire contents of the '287 Application areincorporated herein by reference. The scoring trial described in the'287 application in one arrangement includes a trial device on one endthat approximates the size and shape of the cage implant, a depth stopelement to limit over-insertion into the disc space, and a rotating raspelement to slot the surfaces of the vertebral endplates on the superiorand inferior faces at a controlled distance from the depth stop. Thescoring element is positioned within the trial device at a locationsuitable for creating slots in the vertebral endplates that correspondto entry locations for blades on an anchor plate to penetrate thevertebral endplates. The scoring element is actuated rotationally aboutthe long axis of the instrument by a turning a T-handle at the oppositeend of the device in an oscillating fashion.

While the scoring function of the devices of the '051 Application and'287 Application is beneficial in spinal surgical procedures, certainfeatures in such scoring trials tend to add additional bulk to theinstrument making the devices more cumbersome during use. In some cases,surgeons may opt to use standard trials without scoring capability forthe sizing function, as several passes of various sized trials may berequired to determine the appropriate implant size, and to employ thescoring trial only after the size has been determined. Offering bothforms of trials is costly and undesirable due to the additional spacerequired in sterilization trays.

SUMMARY OF THE INVENTION

It is an object of the subject invention is to provide a compact trialoffering that includes the desirable features of both the standardtrials and scoring trials. A further object is to provide a kitcomprising a plurality of modular scoring trials and a depth stop thatis selectively releasably attachable to each of the modular scoringtrials for a more compact, lower cost instrument offering.

DESCRIPTION OF THE FIGURES

FIG. 1 is a top perspective view of a disc preparation instrument, inaccordance with one embodiment of the present invention, for use infusing together opposing vertebra of a spine.

FIG. 2 is a side elevation view of the disc preparation instrument ofFIG. 1 .

FIG. 3 is a top perspective view of the modular scoring trial of thedisc preparation instrument of FIG.

FIG. 4 is a top perspective exploded view of the modular scoring trialshown in FIG. 3 .

FIG. 5 is a sectional view of a proximal portion of the modular scoringtrial as seen along viewing lines V-V of FIG. 3 .

FIG. 6A is a perspective view of the locking element of the modularscoring trial shown in FIG. 3 .

FIG. 6B is an end view of the locking element of FIG. 6A.

FIG. 6C is a side elevation view of the locking element of FIG. 6A.

FIG. 6D is a longitudinally sectioned view of the locking element asseen along viewing lines VI-VI of FIG. 6C.

FIG. 7 is an exploded top perspective view of the disc preparationinstrument of FIG. 1 showing components of the depth stop of the discpreparation instrument of FIG. 1 .

FIG. 8 is an enlarged longitudinal sectional view of the proximalportion of the disc preparation instrument of FIG. 2 before the T-handleis attached.

FIG. 9A is a perspective view of the T-handle of the disc preparationinstrument of FIG. 1 .

FIG. 9B is a cross sectional perspective view of the T-handle of FIG.9A.

FIG. 10 is the sectional view of FIG. 8 with the T-handle attached.

FIG. 11 is the proximal portion of the disc preparation instrument asseen along viewing lines XI-XI of FIG. 2 .

FIG. 12 is a perspective view showing the distal end of the discpreparation instrument with the trial device being disposed in anintradiscal space between two opposing vertebral bodies of a spine, thevertebral bodies being partially sectioned for clarity, the scoringelement of the trial device being shown in a position forming a scoredlocation in the endplates of the vertebral bodies.

FIG. 13 is side elevational view of a plurality of modular scoringtrials for use in a kit of parts in accordance with one aspect of theinvention, each modular scoring trial having a trial device at thedistal tip of differing heights.

DESCRIPTION OF THE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the invention is therebyintended. It is further understood that the present invention includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the invention aswould normally occur to one skilled in the art to which this inventionpertains.

The present invention contemplates a disc preparation instrument asdepicted in FIGS. 1-3 for use in fusing together opposing superior andinferior vertebra of a spine. Instrument 10 comprises a modular scoringtrial 100, a depth stop 200 that is releasably attached to scoring trial100, and an actuator 300 shown in a particular form as a T-handle. Discpreparation instrument 10 provides a scoring element, as will bedescribed, that scribes vertebral endplates at an appropriateanterior-posterior location for anchor blades on an anterior cervicalcage to engage the vertebral bodies. An inserter which replicates theanterior-posterior distance scribed by the disc preparation instrumentis used to insert the cervical cage into the disc space to the measureddepth so that the blades will be deployed into the slots created by thescoring element. Such an inserter and anterior cervical cage aredescribed in the '287 Application, commonly assigned herewith.Alternatively, the inserter described in U.S. application Ser. No.16/150,344, entitled “Modular Inserter for Anterior Cervical Cage”,filed on Oct. 3, 2018, by Benoit Adamo, et al. (the '344 Application),may also be used in conjunction with the subject disc preparation toolto insert an anterior cervical cage for interbody fusion. The '344Application is assigned to the same assignee as the subject inventionand is incorporated by reference herein in its entirety. It should beappreciated, however, that disc preparation instrument 10 may also beused in interbody fusion procedures in other regions of the spine.

Turning now also to FIGS. 3, 4, 5 and 6A-D, the details of modularscoring trial 100 are described. Scoring trial 100 comprises an elongatestem 102 having a distal end 102 a and a proximal end 102 a and a trialdevice 104 fixedly supported on the distal end 102 a of the stem 102.Elongate stem 102 is of generally cylindrical configuration having apair of diametrically opposing substantially parallel flat surfaces 106extending substantially along the length of stem 102 between distal end102 a and proximal end 102 b. A lumen 108 (see FIG. 10 ) extendssubstantially centrally throughout the length of stem 102, lumen 108opening through both the distal end 102 a and the proximal end 102 b. Acounterbore 110 communicating with lumen 108 is formed at the proximalend 102 b of stem 102, counterbore 110 including an interior surface 110a having a diameter greater than the diameter of lumen 108. Counterbore110 terminates interiorly of stem 102 in a transverse surface 112extending transversely between counterbore 110 and lumen 108. Adjacentdistal end 102 a and disposed distally of flat surfaces 106, elongatestem 102 includes a pair of diametrically opposed stabilizers 102 cprojecting outwardly radially therefrom, the purpose of which will bedescribed hereinbelow.

Trial device 104 has a distal end 114, a proximal end 116, a top surface118 and a bottom surface 120. Top surface 118 has a top opening 118 aand bottom surface 120 has a bottom opening (not shown) similar to topopening 118 a. Trial device 104 supports a rotatably movable scoringelement 122 disposed between distal end 114 and proximal end 116 andhaving a first portion 122 a and a second portion 122 b. The proximalsurface of scoring element 122 is disposed at a predetermined spacing, Sfrom proximal end 116 of trial device 104, as shown in FIG. 3 . Scoringelement 122 is selectively movable from a first position wherein firstportion 122 a and second portion 122 b are both disposed interiorly oftrial device 104 as shown in FIG. 3 to a second position (shown in FIG.12 ) wherein first portion 122 a extends exteriorly of trial device 104through top opening 118 a and second portion 122 b extends exteriorly oftrial device 104 through the bottom opening. First portion 122 a andsecond portion 122 each includes in a particular aspect a rasped scoringsurface along the edges thereof to facilitate scoring of the surfaces ofvertebral endplates, although other abrasive surfaces may also be used.Trial device 104 may be used for the dual purpose of scoring andtrialing but could be used only for scoring. In the dual configuration,trial device 104 is of size and configuration approximating the size andconfiguration of a fusion cage intended for insertion into the discspace. In this regard, trial device 104 has a maximum height, H betweentop surface 118 and bottom surface 120, as illustrated in FIG. 2 . Trialdevice 104 may also be formed to taper downwardly toward distal end 114defining trial device 104 to have a lordotic configuration, as also seenin FIG. 2 .

As illustrated in FIG. 4 , an elongate shaft 124 having a distal end 124a and a proximal end 124 b extends within lumen 108 of stem 102.Elongate shaft 124 is rotatable but not axially translatable withinlumen 108. Axial translation of shaft 124 relative to stem 102 isprevented by a pair of pins 126 extending through a pair of openings 127extending through proximal end 102 b of stem 102 and disposed in agroove 128 extending around the circumference of shaft 124. Distal end124 a includes an engagement feature 124 c for extending into trialdevice 104 and engaging scoring element 122. In one particulararrangement, engagement feature 124 c is a multi-faceted drive withopposing flat surfaces, sized and configured to engage with acomplementary sized and configured opening 122 c formed in scoringelement 122. Shaft 124 has at its proximal end 124 b a drive element 130for engagement with actuator 300 for rotating shaft 124 and scoringelement 122, as will be described. Drive element 130 includes anon-circular configuration and, in a particular arrangement, comprises asquare drive having four substantially flat mutually orthogonalengagement surfaces 130 a. At least one of such flat surfaces 130 a isformed to be in alignment with a flat surface of engagement feature 124c in a manner to fully retain scoring element 122 within trial device104 when scoring element 122 is in the first position as describedhereinabove. Shaft 124 is of length such that when engagement feature124 c is in engagement with scoring element 122, drive element 130 isdisposed within counterbore 110 at the distal end 102 b of stem 102, asdepicted in FIG. 5 .

Shaft 124 includes a generally cylindrical locking element supportsurface 131 between circumferential groove 128 and drive element 130.Disposed on support surface 131 and within counterbore 110 at the distalend 102 b stem 102 is a spring element 132 and a locking element 134. Ina particular arrangement, spring element 132 is a coil spring ofgenerally cylindrical configuration having a distal end 132 a and aproximal end 132 b. As shown in more detail in FIGS. 6A-D, lockingelement 134 is of generally cylindrical configuration having a distalend 134 a, a proximal end 134 b and an interior surface 134 ctherebetween. Locking element 134 includes a pair of diametricallyopposed substantially parallel exterior flat surfaces 134 d formed in anouter wall 134 e of locking element 134. As such, flat surfaces 134 ddefine a pair of recesses 134 f that extend for a length L betweendistal end 134 a and proximal end 134 b, as shown in FIG. 6D. Lockingelement 134 comprises on its interior surface 134 c at its proximal end134 b a locking surface 134 g that is complementary with thenon-circular configuration of drive element 130 at the proximal end 124b of elongate shaft 124. In a particular configuration, locking surface134 g comprises a square socket including four substantially flatmutually orthogonal interior engagement surfaces 134 h, as shown inFIGS. 6A and 6B, each surface 134 h being sized and configured toreleasably engage a respective flat surface 130 a of drive element 130.Exterior flat surfaces 134 d are oriented to be substantially parallelwith two of said engagement surfaces 134 h and with flat surfaces 106 ofstem 102 so as to provide proper orientation of shaft 124 relative tostem 102 when locking element 134 is assembled to stem 102.

Upon assembly with shaft 124, spring element 132 is initially introducedinto counterbore 110 at proximal end 102 b of stem 102 until springelement distal end 132 a contacts interior transverse surface 112, asseen in FIG. 5 . Locking element 134 is then introduced into counterbore110 with distal end 134 a engaging spring element proximal end 132 b andcompressing spring element 132 against transverse interior surface 112,as shown in FIG. 5 . A pair of pins 136 is introduced through openings138 formed through proximal and 102 b of stem 102 to movably attachlocking element 134 to stem 102, with pins residing in locking elementrecesses 134 f, as shown in FIG. 5 . Pins 136 are disposed sufficientlyclose to locking element exterior flat surfaces 134 d to substantiallyprevent rotational movement of locking element 134 relative to stem 102within counterbore 110 while allowing relative axial translation. Theextent of axial translation of locking element 134 within counterbore110 is governed by the length L of recesses 134 f formed in lockingelement 134. As depicted in the position shown in FIG. 5 , spring 132 iscompressed within counterbore 110 thereby providing an axial bias forceagainst locking element 134 toward the proximal end of stem 102 withpins 136 residing in recesses 134 f maintaining the bias force. In thisfirst position, flat surfaces 134 h of locking element 134 are inreleasable engagement with flat surfaces 130 a of drive element 130,thereby preventing rotation of shaft 124 relative to stem 102 while thebias force is applied. Upon application of an axial force in the distaldirection against locking element 134 sufficient to overcome the biasforce of spring element 132 as will be described, locking element 134 ismoved in a distal direction to a second position whereby flat lockingsurfaces 134 h of locking element 134 are disengaged from drive element130 to thereby allow rotation of elongate shaft 124 relative to stem102.

To releasably attach depth stop 200 to scoring trial 100, an attachmentlocation 140 is provided on elongate stem 102 at the proximal endthereof, as shown in FIG. 3 . In a particular arrangement, attachmentlocation 140 comprises a pair of diametrically opposed locking grooves140 a disposed between the respective openings 127 that are provided toreceive pins 126. Attachment location 140 is set at a fixedpredetermined distance, X from a first location on trial device 104,such as proximal end 116, as illustrated in FIG. 3 . It should beappreciated that the first location on trial device 104 may also bedefined by scoring element 122. Grooves 140 a of attachment location 140are oriented in one particular arrangement to be on a line that issubstantially parallel with the height, H of trial device 104 of scoringtrial 100.

Turning now also to FIGS. 7 and 8 , further details of the depth stop200 are described. Depth stop 200 comprises a handle 202, an adjustmentknob 204, an elongate sleeve 206, a center shaft 208 and a bushing 210.Handle 202 is generally cylindrical having a distal end 202 a, aproximal end 202 b, and an interior surface 202 c within whichadjustment knob 204 and center shaft 208 are disposed. Handle 202includes a window 212 extending through an exterior surface to exposeportions of adjustable knob 204. Interior surface 202 c of handle 202comprises internal threads 214 disposed adjacent the distal end 202 a,as illustrated in FIG. 8 . Threads 214 have a first predetermined pitch,such as 2 mm, with threads 214 being oriented in a first direction as aleft-handed thread.

Elongate sleeve 206 is generally cylindrical having a distal end 206 aand a proximal end 206 b. Sleeve 206 has a partially open channel 216extending generally centrally through sleeve 206 and through distal end206 a and proximal end 206 b. Distal end 206 a terminates in a stop 218for measuring the depth of scoring element 122 from an exterior surfaceof a vertebra when the trial device 104 is inserted within anintervertebral disc space, as will be described. In a particulararrangement, stop 218 is defined by pair of opposed laterally spacedshoulders 218 a having substantially flat interior surfaces. Each stop218 may have an internally formed pocket 218 b (see FIG. 12 ) forreceipt of stabilizers 102 c, as will be described. Channel 216 is ofsize and configuration to receive elongate stem 102 of modular scoringtrial 100 such that flat surfaces 106 of scoring trial 100 are disposedclosely adjacent flat surfaces of opposed shoulders 218 a for properorientation of trial device 104 relative to shoulders 218 a. Proximalend 206 b of sleeve 206 includes an attachment portion 220 including acircumferential groove 222.

Adjustment knob 204 is of generally cylindrical configuration having adistal end 204 a and a proximal end 204 b. Adjustment knob 204 includesexternal threads 224 adjacent distal end 204 a that are threadablycoupled with handle internal threads 214, threads 224 having the samefirst predetermined pitch and left-handed direction as handle internalthreads 214 establishing a first threaded connection, as will bedescribed. Proximal end 206 b of sleeve 206 is coupled to distal end 204a of adjustment knob 204 by a set of pins 226 extending through sleeve206 and into groove 222. Such coupling enables adjustment knob 204 andsleeve 206 to move axially jointly while allowing for rotationalrelative movement therebetween, movable stop 218 being affixed at thedistal end 206 a of sleeve 206. Interior surface 204 c has adjacent theproximal end 204 b of adjustment knob 204 internal threads 228, asillustrated in FIG. 8 . Threads 228 have a second predetermined pitch,such as 2 mm, with threads 228 being right-handed threads and therebyoriented in a second direction, opposite the first direction of internalthreads 214 of handle 202. In a particular arrangement, the secondpredetermined pitch of threads 228 is equal to that of the firstpredetermined pitch of threads 214. Adjustment knob 204 includes aplurality of axially extending circumferentially spaced splines 230 thatare exposed through handle window 212, splines 230 facilitating themanual rotation of adjustment knob 204, as will be described.

Center shaft 208 is generally cylindrical having a distal end 208 a, aproximal end 208 b and an interior surface 208 c. Distal end 208 acomprises external threads 232, threads 232 having the same secondpredetermined pitch and right-handed direction as internal threads 228of adjustment knob 204 for engagement in a second threaded connection,as will be described. An indicator device 234 at the proximal end 208 bof center shaft 208 comprises a plurality of markings 234 a, such asnumerical indicia and gradations. Center shaft 208 further includes atits proximal end 208 b a connection portion 236 for releasableattachment to actuator 300, as will be described. Connection portion 236includes a pair of diametrically opposed substantially parallel flatsurfaces 238 at proximal end 208 b and a pair of diametrically opposedgrooves 240 extending between flat surfaces 238 on either side ofconnection portion 236. Center shaft 208 in addition includes adjacentproximal end 208 b a series of detent grooves 242 formed diametricallyapart on the outer surface of center shaft 208, detent grooves 242 beingspaced at predetermined axial intervals to correspond with increments ofdepth stop measurements as denoted by markings 234 a of indicator device234.

Center shaft 208 includes a pair of diametrically opposed openings 244that are each formed to hold therein a ball bearing 246. Ball bearings246 define a ball bearing lock for releasably locking center shaft 208to scoring trial 100, as will be described. Each opening 244 extendsradially through the wall of center shaft 208 and through interiorsurface 208 c. Each ball bearing 246 has a diameter slightly greaterthan the wall thickness of center shaft 208 and is retained in arespective opening 244 such that ball bearings 246 may slightly move inthe radial direction. In one position, each ball bearing 246 has acircumferential portion extending radially inwardly beyond interiorsurface 208 c with a diametrically opposite circumferential portionbeing disposed within the wall of center shaft 208. In a secondposition, a circumferential portion of each ball bearing 246 extendsradially outwardly beyond the exterior surface of center shaft 208 withthe diametrically opposite circumferential portion being disposed withinthe wall of center shaft 208. Opposed openings 244 and ball bearings 246are disposed on a line that is substantially perpendicular to opposingflat surfaces 238 at the distal end 208 b of center shaft 208.

Bushing 210 is generally cylindrical having a distal end 210 a, aproximal end 210 b and an interior surface 210 c. Interior surface 210 chas a counterbore 210 d at the distal end 210 a of bushing 210. Theinner diameter of counterbore 210 d is greater than the inner diameterof inner surface 210 c. Proximal end 210 b of bushing 210 includes apair of axially spaced circumferentially extending grooves 248 and 250.Groove 250 includes therewithin a pair of diametrically opposed openings252 that are each formed to house therein a ball bearing 254. Each ballbearing 254 is resiliently retained in a respective opening 252 by aspring member, such as a C-clip 256 that is retentively supported withingroove 250. C-clip 256 applies a radially inward bias force to ballbearings 254 in a manner that allows a circumferential portion of eachball bearing 254 to resiliently radially move inwardly and outwardly ofinterior surface 210 c of bushing 210. As such, ball bearings 254 definea spring biased ball detent with grooves 242 on center shaft 208, aswill be described A locking ring 258 is retained in groove 248 forconnecting bushing 210 to interior surface 202 c of handle 202 in theaxial direction, as will be described.

Turning now to FIGS. 9A and 9B, details of actuator 300 are described.Actuator 300 comprises a generally cylindrical central hub 302 includinga drive portion 304 projecting axially therefrom. Drive portion 304 hasa drive surface 304 a configured to cooperatively mate with driveelement 130 at the proximal end 124 b of elongate shaft 124 of scoringtrial 100. Drive surface 304 a includes a non-circular configurationand, in a particular arrangement, comprises a square drive having foursubstantially flat mutually orthogonal engagement surfaces 304 b thatdefine a square socket of size and configuration to interface with thefour substantially flat engagement surfaces 130 a of drive element 130.Central hub 302 comprises a pair of diametrically opposed flanges 306projecting axially distally therefrom, each flange 306 being defined byan undercut groove 308, as seen more particularly in FIG. 9B. Opposingflanges 306 are substantially parallel to each other with each flange306 being oriented substantially parallel to one of flat surfaces 304 b.Actuator 300 includes a pair of manually graspable extensions 310projecting radially oppositely from central hub 302 and defining therebya T-handle. Rotation of actuator 300 rotates elongate shaft 124 andthereby scoring element 122 of scoring trial 100. Extensions 310 are inalignment with each other and with flanges 306 to provide a visualindication of the orientation of scoring element 122 of scoring trial100 in use. Central hub 302 includes at its distal end a contact surface304 c for contacting proximal end 134 b of locking element 134 to applyan axial force thereto in the distal direction, as will be described.

The assembly of the components to form depth stop 200 is now describedwith continued reference to FIGS. 7 and 8 . Sleeve 206 is rotatablyattached to adjustment knob 204 by pins 226. This subassembly isintroduced through handle 202 from proximal end 202 b to 202 a is shownby phantom line 260 in FIG. 7 with movable stop 218 being welded tosleeve 206 thereafter. External threads 224 of adjustment knob 204 arethreadably engaged with internal threads 214 of handle 202 therebyforming the first threaded connection. Center shaft 208 containing ballbearings 246 is introduced into threaded knob 204 such that externalthreads 232 on center shaft 208 threadably engage internal threads 228of adjustment knob 204 until proximal end 208 b of center shaft 208 isapproximately flush with proximal end 202 f of handle 202, as depictedin FIG. 8 , thereby establishing the second threaded connection. Bushing210 with attached C-clip 256 residing in groove 250 and resilientlyholding ball bearings 254 in openings 252 is attached to the interiorsurface 202 c of handle 202 by snapping locking ring 258 into a groove202 d formed in interior surface 202 c at the proximal end 202 b ofhandle 202. In this condition as shown in FIG. 8 , ball bearings 246housed in the wall of center shaft 208 are in radial alignment withcounterbore 210 d of bushing 210, thereby allowing ball bearings 246 toradially float such that a circumferential portion of each ball bearing246 extends within counterbore 210 while a diametrically opposingcircumferential portion does not extend radially interiorly beyondinterior surface 208 c. In this condition, depth stop 200 is ready toreceive scoring trial 100. Once in place, sleeve 206, handle 202 andbushing 210 are all suitably keyed with respect to each other in amanner to maintain relative radial alignment.

With continued reference to FIGS. 7-8 , and now also to FIGS. 10-11 ,the attachment of depth stop 200 and scoring trial 100 is described.Scoring trial 100 is introduced into depth stop 200 by initiallyradially introducing flat surfaces of shoulder 218 a over flat surfaces106 of elongate stem 102. Elongate stem 102 is then slid proximallyaxially within channel 216 and into opening 202 e at the distal end 202a of handle 202 until proximal end 102 b abuts counterbore 208 d ofcenter shaft 208, as shown in FIG. 8 . During such proximal movement ofstem 102, stabilizers 102 c are received within pockets 218 b of eachstop 218, as shown in FIG. 12 . Such interaction between stabilizers 102a and pockets 218 b substantially prevents rotation of stem 102 relativeto depth stop 200, thereby maintaining proper orientation of trialdevice 104 relative to shoulders 218 a. At this point, attachmentgrooves 140 a are in radial alignment with ball bearings 246 containedin center shaft 208. Adjustment knob 204 is then rotated clockwisethrough window 212 of handle 202 thereby activating the first and secondconnections, as described hereinabove. Such clockwise rotation causesadjustment knob 204 via the second threaded connection between threads228 and 232 to move adjustment knob 204 axially in a distal directionrelative to elongate stem 102. Additionally, such clockwise rotation ofadjustment knob 204 via the first threaded connection between threads214 and 224 causes handle 202 to also move axially distally relative toelongate stem 102. As a result, bushing 210 being axially attached tohandle 202 also moves in a distal direction such that counterbore 210 dis no longer radially aligned with ball bearings 246, as illustrated inFIG. 10 . Rotation of adjustment knob 204 can continue until springloaded detent ball bearings 254 engage the most distal detent grooves242. The engagement of ball bearings 254 in respective detent grooves242 creates a surmountable ball detent that provides tactile feedbackand an audible click. The axial distal movement of handle 202 causesinterior surface 210 c of bushing 210 to engage ball bearings 246 andurge such ball bearings 246 into the locking grooves 140 a of elongatestem 102, thereby establishing a rigid releasable locking connectionbetween depth stop 200 and elongate stem 102 of scoring trial 100. Suchlocking connection is released by rotating adjustment knob 204 in acounterclockwise movement thereby proximally moving bushing 210 to theposition of FIG. 8 whereby counterbore 210 d is in radial alignment withball bearings 246. Scoring trial 100 may then be readily removeddistally from depth stop 200.

Referring again to FIGS. 9A, 9B and also to FIGS. 10-11 , the releasableattachment of actuator 300 is described. Actuator 300 is releasablycoupled to drive element 130 of elongate shaft 124 of scoring trial 100in a manner to rotate scoring element 122 for scoring opposing vertebralendplates in preparation for receipt of anchor blades of an interbodyfusion cage. To attach actuator 300 to drive element 130, actuator 300is initially positioned with opposing flanges 306 oriented to be inalignment with opposing flat surfaces 238 on connection portion 236 ofcenter shaft 208. In this orientation, flanges 306 may slide over flatsurfaces 238 thereby allowing axially projecting drive portion 304 toextend into the interior of center shaft 208 at the proximal end 208 bthereof. Contact surface 304 c at the distal end of drive portion 304contacts proximal end 134 b of locking element 134 to apply an axialforce thereto in the distal direction. Such axial force is sufficient toovercome the bias force applied in the proximal direction againstlocking element 134 by spring element 132. Under the application of theaxial force provided by the distal movement of actuator 300, lockingelement 134 is urged in the distal direction releasing the integratedlock and exposing drive element 130, allowing attachment of square-drivesurface 304 a with square-drive element 130, as shown in FIG. 11 . Inthis first position, actuator 300 may also be removed proximally fromcenter shaft 208.

At this point, rotation of T-handle 300 in either the clockwise orcounterclockwise directions to a second position will cause flanges 306on actuator hub 302 to engage grooves 240 extending between flatsurfaces 238 on either side of connection portion 236 of center shaft208. Such engagement prevents removal of the T-handle until it isreturned to the original first position or approximately 180 degreesopposite the original first position. Rotation of T-handle 300 in eitherdirection rotates elongate shaft 124 and thereby scoring element 122 ina manner to score surfaces of opposing vertebral body endplates. Oncethe T-handle 300 begins to rotate it cannot be removed from center shaft208 unless it is returned to its original location or 180 degreesopposite the original location. This arrangement alerts the surgeon tothe position of the scoring element 122 within trial device 104 as theT-handle 300 may only be removed when the scoring element 122 iscollapsed and the integrated lock 134 is enabled. Once the T-handle isreturned to the original first position, T-handle 300 may be removed,and the surgeon may safely remove scoring trial 100 by pullingproximally outwardly on depth stop handle 200 without concern thatscoring element 200 remains penetrated into the vertebral body.

Having described the disc preparation instrument 10, the function andoperation of indicator device 234 is now described with particularreference to FIGS. 7-8 and FIG. 2 . Indicator device 234 is operablewith the axial distal movement of handle 202 relative to center shaft208 to provide a visual indication of a plurality of selectabledistances that stop 218 may move relative to trial device 104. As notedhereinabove, clockwise rotation of adjustment knob causes adjustmentknob 204 via the second threaded connection between threads 228 and 232to move adjustment knob 204 axially in a distal direction relative toelongate stem 102 which is axially affixed to trial device 104 at thedistal tip of elongate stem 102. Additionally, such clockwise rotationof adjustment knob 204 via the first threaded connection between threads214 and 224 causes handle 202 to also move axially distally relative tocenter shaft 208 which is releasably axially locked to elongate stem 102by the ball bearings 246. Distal movement of adjustment knob 204 causessleeve 206 and attached stop 218 to move distally relative stem 102 andthereby to a first location on trial device 104. It should be understoodthat counterclockwise rotation of adjustment knob 204 will causeadjustment knob 204 and handle 202 to move proximally relative toelongate stem 102 at the rates as described herein.

Such first location on the trial device 104 may be its proximal end 116,as shown in FIG. 2 . Each distance, D, for example, that stop 218 isselectively spaced from proximal end 116 of trial device 104 isindicated by a different marking 234 a that will be visually observableupon the axial distal movement of handle 202 which progressively exposesmarkings 234 a at the proximal end of center shaft 208 relative to areference element on depth stop 200. Such reference element in oneapproach is defined by end surface 210 e at the proximal end of bushing210. Alternatively, since bushing 210 is fixed axially relative tohandle 202, the reference element may be defined by end surface 202 f atthe proximal end of handle 202. In a particular arrangement, markings234 a are two millimeters apart for ease of viewing but indicateone-millimeter increments of depth stop motion. This is accomplished viathe two threaded connections (214/224 and 228/232) described above ofsubstantially equal pitch but opposing directions. As such, when theadjustment knob 204 is rotated, relative axial translation between thehandle 202 and center shaft 208 with markings 234 a thereon occurs attwice the rate of axial translation between stop 218 and trial device104. As a result, indicator device 234 provides an amplified indicationof each of the selectively different distances, D between stop 218 andproximal end 116 of trial device 104. Such amplified indication allows asurgeon to more readily appreciate the location at which fusion cage maybe placed in an intradiscal space, which is typically measured inmillimeters and is relatively difficult to visually discern. It shouldbe understood that while the threaded connections (214/224 and 228/232)are formed in opposing directions with each threaded connection having apitch of 2 mm, similar differential rates of movement as describedherein may be achieved with the threaded connections being in a commondirection but of different pitches.

In this particular arrangement, indicator device 134 includes threeindicia, denoted as “0”, “1”, and “2”. The spacing in indicator device234 between each of these markings is two millimeters, each of whichrepresents a distance, D of 1 mm increment. The “0” marking may indicatea distance, D of approximately 2 mm, the “1” marking a distance, D ofapproximately 3 mm, and the “2” marking a distance, D of approximately 4mm. As illustrated in FIG. 2 , marking “2” is shown, indicating thatstop 218 is measured at a distance, D of approximately 4 mm from trialdevice proximal end 116. Where the predetermined spacing, S betweentrial device proximal end 116 and the proximal surface of scoringelement 122 is set, for example at 2 mm, the distance then between stop218 and the proximal surface of scoring element 122 is determined to be6 mm. As handle 202 translates distally relative to center shaft 208,spring biased detent balls 254 sequentially engage detent grooves 242that are spaced apart at predetermined axial intervals corresponding tomarkings 234 a on indicator device 234, provide tactile feedback and/oran audible click to the surgeon as each interval is reached. In theexample shown in FIG. 2 where the marking “2” is shown detent balls 254would be engaged in the most proximal set of grooves 242, and in themost distal set of grooves 242 when the indicator device 234 reads “0”.

Having described the disc preparation instrument 10, a method for use inan interbody fusion procedure is described, with particular reference toFIG. 12 . In one particular approach, disc preparation instrument 10 isused to prepare an intradiscal space for fusing together a superiorvertebra 400 and an inferior vertebra 402 in the cervical region of thespine in a procedure known as a Smith-Robinson approach. It should beappreciated, however, that disc preparation instrument 10 may also beused in interbody fusion procedures in other regions of the spine.Superior vertebra 400 includes an inferior endplate 400 a, a vertebralbody 400 b, and an exterior anterior surface 400 c. Inferior vertebra402 includes a superior endplate 402 a, a vertebral body 402 b and anexterior anterior surface 402 c (not seen). Superior endplate 400 a andinferior endplate 402 a define an intradiscal space 404 therebetween.Endplates 400 a, 402 a consist primarily of relatively hardbony/cartilaginous material that is often difficult to penetrate forfixing fusion implants for interbody fusion purposes. In the cervicalspine procedure, access to the spine is often provided by forming anincision through the anterior portion of the patient's neck to exposesuperior and inferior vertebrae 400,402. As such, exterior surfaces 400c, 402 c of superior vertebra 400 and inferior vertebra 402,respectively, are anterior surfaces. A suitable discectomy is performedto provide an appropriate disc space 404 for receipt of a cage of thetype described in the '051 Application or the '287 Application, each ofwhich is incorporated by reference in its entirety herein. It should beunderstood that access may be provided in other approaches, such asposterior or lateral in lumbar/thoracic procedures, as well as in otherspinal surgeries, such as corpectomies

Disc preparation instrument 10 is used to suitably prepare opposingvertebral endplates 400 a, 402 a for receipt of a desired cage. Discpreparation instrument 10 is used to introduce trial device 104 at thedistal tip thereof as described hereinabove into the disc space 404using suitable imaging techniques, such as fluoroscopy. Such imagingincludes a side view from the lateral perspective so that the depth oftrial device 104 along the anterior-posterior (A/P) direction may beobserved. Prior to introduction of the trial device 104 into the discspace the surgeon may set the indicator device 134 at a reading of “0”,establishing a depth, D of approximately 2 mm. Should the surgeondetermine that deeper penetration of a fusion cage is desired, the depthmay be adjusted by rotating adjustment knob 204. Counterclockwiserotation causes adjustment knob 204 and sleeve 206 axially attachedthereto to move proximally away from vertebral bodies 400, 402, allowingthe fusion cage to be inserted deeper into the intradiscal space 404until stop 218 at the distal end of sleeve 206 engages exterior surfaces400 c and 402 c, as depicted in FIG. 12

Vertebral endplates 400 a, 402 a are then scored with disc preparationinstrument 10. Scoring is effected by the rotation of T-handle 300 whichrotates scoring element 122 from the first position to the secondposition, as illustrated in FIG. 12 . Such rotation causes the abrasiveedges of first portion 122 a and second portion 122 b of scoring element122 to cut a slot 406 into endplates 400 a, 402 a. Complete penetrationof slots 406 into the bony/cartilaginous endplates 400 a, 402 a may notbe necessary as slots 406 at least provide a weakened, secured locationto facilitate entrance of anchor plates on a fusion cage. T-handle 300may be rotated clockwise or counterclockwise several times if necessaryin order to suitably form scored location 406. After completion of thescoring procedure, disc preparation instrument 10 may be fully removedby manually pulling handle 202 in a proximal direction.

As can be appreciated, a surgeon may choose to use the scoring trial 100with integrated scoring element 122 and integrated lock 134 for thesizing function, and once the scoring trial 100 has been deemedappropriate in size, attach the depth stop 200 without removing scoringtrial 100 from the surgical site. Upon attachment, the surgeon canadjust the position of the depth stop 200 relative to trial device 100by rotating depth stop adjustment knob 204. In performing this action,the depth stop handle 202 is automatically coupled to the scoring trial100 via the ball bearing lock 246. Once the stop 218 is seated againstthe vertebral body, the surgeon can read the depth measurement from thegraduations or markings located on the indicator device 234 at theproximal end of center shaft 208 that protrudes proximally from theproximal end of handle 202 and note this measurement for subsequentcorrelation with a cage inserter instrument, such as the inserterdescribed in the '344 Application. In this regard, a plurality ofmodular scoring trials 100 as shown in FIG. 13 , each having a trialdevice 104 of different heights, for example H₁, H₂ and H₃, may beprovided in a kit. Each scoring trial 100 may be selectively releasablyattached to a single depth stop 200. Each scoring trial 100 of the kithas an attachment location 140 on the stem 102 that is set at a fixedpredetermined distance, X such as from attachment location 140 toproximal end 116 of a respective trial device 104. The fixedpredetermined distance, X of each such modular scoring trial 100 isapproximately the same. Further, the drive element 130 of the elongateshaft 124 of each modular trial 100 has substantially the sameconfiguration and size.

As such, a variety of scoring trials 100 may be made available for usein assessing the size of the disc space 404 for selection of anappropriately sized fusion cage. A single T-handle 300 may be includedin the kit together with a plurality of differently sized fusion cagesto allow for selection based upon the assessment of disc space 406.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, it should be understood that suchdescription is illustrative and not limiting. For example, an instrumentfor providing an amplified indication of a measured distance may be usedin other surgeries where small dimensions are to be measured, typicallyin millimeters. Such surgeries, other than spinal surgery as describedherein include, but are not limited to, maxillofacial surgeries andextremity surgeries, such as those involving the wrist. In such use, theinstrument would comprise an elongate member having a distal end and aproximal end, the distal end of the elongate member including a firstpoint of measurement and configured to be positioned within tissue of apatient. A movable stop having a surface defining a second point ofmeasurement movable relative to the elongate member would be included,such stop being configured to contact a suitable surface of the patient.The movable stop would be movable to a plurality of selectable distancesbetween the first point and the second point. An indicator device asdescribed herein operable with the movement of the stop would beincluded to provide an amplified visual indication of each of theplurality of selectable distances

It should therefore be understood that various changes, modificationsand further applications may be made without departing from the spiritof the invention and the scope of the appended claims.

What is claimed is:
 1. A depth stop for use in providing an amplifiedindication of a measured distance a surgical element is introduced intoa disc space between two opposing vertebrae of a spine during spinalsurgery, said depth stop comprising: a handle having a distal end and aproximal end, said proximal end defining a reference element thereon,said handle comprising internal threads of a first pitch and firstdirection adjacent the distal end; an adjustment knob having a distalend and a proximal end, said adjustment knob including external threadsadjacent the distal end thereof and internal threads adjacent theproximal end thereof, said external threads being in the same firstdirection as and of approximately the same pitch as said internalthreads of said handle and being threadably engaged therewith to definea first threaded connection, said internal threads of said adjustmentknob having a second pitch and a second direction, said second directionbeing opposite said first direction, a sleeve attached to the distal endof said adjustment knob, said sleeve having a stop thereon movable withsaid adjustment knob, said stop being sized and configured to engage anexterior surface of one of said vertebrae; and a center shaft having adistal end and a proximal end, said center shaft having external threadsadjacent said distal end, said external threads being in the same seconddirection as said internal threads of said adjustment knob and ofsubstantially the same pitch, said external threads of said center shaftbeing threadably engaged with said internal threads of said adjustmentknob to define a second threaded connection, said center shaft includingat said proximal end an indicator device comprising a plurality ofmarkings, wherein upon rotation of said adjustment knob on said centershaft in one direction, said adjustment knob and thereby said stop movedistally relative to said center shaft at one rate and said handle andthereby said reference element thereon moves distally on said adjustmentknob relative to said center shaft and thereby said indicator devicemarkings at a second rate greater than said first rate.
 2. The depthstop of claim 1, wherein the pitch of said first and said secondthreaded connections is substantially equal, thereby causing said secondrate to be approximately twice said first rate.
 3. The depth stop ofclaim 2, wherein said surgical element is a trial device sized andconfigured to be inserted into said disc space.
 4. An instrument forproviding an amplified indication of a measured distance between twopoints in surgery, said instrument comprising: an elongate member havinga distal end and a proximal end, the distal end of said elongate memberincluding a first point of measurement and configured to be positionedwithin tissue of a patient, a movable stop having a surface defining asecond point of measurement movable relative to said elongate member,said stop being configured to contact an exterior surface of saidpatient, said movable stop being movable to a plurality of selectabledistances between the said movable first point and said second point;and an indicator device comprising a plurality of markings, saidindicator device being operable with movement of said stop to provide anamplified visual indication of each of said plurality of selectabledistances, wherein said elongate member supports a reference elementmovable with movement of said movable stop relative to said indicatordevice to expose said markings of said indicator device at a rategreater than a rate of movement of said movable stop.
 5. The instrumentof claim 4, wherein said amplified indication is effected by first andsecond threaded connections between said elongate member and saidmovable stop.
 6. The instrument of claim 5, wherein said first andsecond threaded connections are configured to be in opposite directionscausing said movable stop and said reference element to move in the samedirection relative to said indicator device.
 7. The instrument of claim6, wherein a pitch of said first and second threaded connections issubstantially equal, thereby causing said reference element to move at arate approximately twice the rate movement of said movable stop.
 8. Theinstrument of claim 7, wherein said instrument is an instrument for usein fusing together a superior vertebra and an inferior vertebra, thesuperior vertebra including an inferior endplate and a vertebral body,the inferior vertebra including a superior endplate and a vertebralbody, the superior and inferior endplates defining a disc spacetherebetween, said elongate member having at its distal end an elementsized and configured for insertion into said disc space, said firstpoint of measurement being located on said element.